The present invention is directed to a valve assembly for a bag. More specifically, the valve assembly is directed for use in what the bag-making industry refers to as pasted valve bags of a tubular construction wherein opposite ends are typically provided with satchel ends that are sealed prior to filling except for an opening at the valve assembly itself.
Even with more particularity, the invention is directed toward improvements to four member valve assemblies of the type that are self-closing upon the completion of the filling of the bag.
Prior art four member valve constructions utilizing a two-part upper insert and a two-part lower insert, such as disclosed in German Patent No. 2935971, have achieved a certain degree of success in valve closure effectiveness upon the filling of the bag and the prevention of sifting or dusting caused by blowback around the packing area. Such construction of a four member valve assembly has required two inserts, each of which comprises a paper blank and a substantially thinner plastic film member. The present invention improves upon this type of valve assembly by attaining: greater strength; minimal chance of plies or insert members sticking together caused at the inside by adhesive squeeze-out or bleed through; a better self-closing flap-valve-type closure; and enhanced tear-resistance at the corner ear fold or corner tuck where the valve is located. By enhancing the strength of the valve assembly, tearing, splitting and rupturing during insertion and retraction of a filing nozzle are substantially eliminated. Channeling of the product out of the valve assembly between the valve assembly and the folded plies of the bag is also virtually eliminated. Less drag resistance against the insertion spout or nozzle is also achieved. While the use of a thin plastic for a flap-valve closure, such as with polyethylene film, has achieved a certain degree of effectiveness in the prior art, it is further a goal of the invention to eliminate the utilization of a thin plastic film and provide a four member valve assembly entirely made of paper. It has also been found that it is important to step the members of the upper and lower sub-assemblies of the valve assembly in the lateral direction. This stepping, or shingling, also achieves a greater degree of overlap for each of the upper and lower sub-assemblies extending outside the fold lines of the satchel ends. It has also been discovered that stepping the members of each sub-assembly with respect to each other inwardly of the bag provides improved valve closure. Thereby, not only are better trapping abilities provided but the improved valve-assembly herein will provide a better closure with less pasting/adhesive. The invention also takes advantage of the adhesive effectiveness of well known starch based adhesives for affixing the valve assembly to the plies of the paper bag, which adhesive is preferable in the paper bag making industry since hot melt glues or sonic sealing is not required.
The prior art valve assembly as shown in said German Patent No. DE2935971 provides an upper sub-assembly, or insert, that has over-lying flush-cut paper and plastic film members. The present invention improves upon this by reducing the amount of material required for the valve assembly by longitudinally stepping back one of the members at an upper or first sub-assembly.
Accordingly, it is a primary goal of the invention to provide a four member valve closure assembly comprising a first, or upper, two member sub-assembly nestable within a second, or lower, two member sub-assembly to substantially eliminate sifting from the valve during and after filling. It is accordingly an additional goal of the invention to provide such a valve assembly that achieves superior self-closing capability as the bag reaches and becomes filled with a product.
It is also an allied goal of the invention to attain superior strength due to an improved folded arrangement for the valve members. It is an additional goal to achieve this strength while still affording excellent self-closure due to improved inner member pliability as the filling product is forced against the valve assembly during bag filling and valve closure. It is a concomitant goal to provide improved sift-proofness by virtue of a lateral and longitudinal stepping design and formation of product-trapping pockets.
It is the further goal of the invention to provide a self-closing sift-proof valve assembly that may be used with very finely comminuted products of less then one micron in particle size, such as found in carbon black. Accordingly, the invention provides sift-proofness and self-closablity for products ranging from course granulated material, such as salt, or sugar, down to powdered milk sized granulation and even to these very fine particle sizes of less then one micron.